There is a threshold level to everything - here:
"Now there's no doubt that the brain is plastic, able to rewire itself in response to damage or training, and that it's more so than was generally believed, say, 20 years ago. It's clearly an important and interesting field, but a little caution is warranted. Neuroplasticity can't fix everything.
If the brain were infinitely plastic, brain damage would be no big deal. You'd get over it pretty quickly, so long as some of your brain was intact and able to rewire itself to compensate. Unfortunately, that's rarely what happens. Well, unfortunately unless you're a neurologist; they'd be out of a job if the brain otherwise...
Swiss neurologists Bindschaedler et al have provided a nice example of the limits of neuroplasticity in a new paper: Growing up with bilateral hippocampal atrophy:From childhood to teenage."
So VJ's brain couldn't rewire itself to compensate for the lack of a hippocampus, despite the fact that the damage occurred at birth, and the brain is considered to be at its most plastic during childhood.
This is not all that surprising really. The hippocampus is a unique region, containingspecialized circuitry which is just not found anywhere else in the brain. Most of the evidence for large-scale neuroplasticity concerns the cerebral cortex. When part of the cortex is damaged, other cortical areas can sometimes compensate for the loss: but the cortex can't turn itself a substitute hippocampus."